I'm conflicted. On one hand, I've seen some very interesting, very compelling, street photography. On the other hand, though legal, I would feel uncomfortable about taking photos of anyone without their permission even if they have no (legal) expectation of privacy. It just feels very wrong.
That said, I've seen candid moments that I so wish I could have captured. The one that I'll always remember happened on a sidewalk in Kanab probably 30 years ago. For those who don't know, Kanab is not far from large FLDS (polygamist) communities where young women are kept isolated from modern society (at least they were at that time). An FLDS man was herding 2 very young women down the sidewalk. He held their hands and was practically dragging them along. Though it was really hot, they were dressed in 19th Century prairie garb, heavy gingham skirts down to their toes, long puffy sleeves, hair French-braided. They were clearly excited to be in town, trying to take in everything there was to see. It looked as if this was their first time in the outside world and they didn't want to miss anything. Their escort (assuming it was their husband) was all business, hurrying them past all the tourists and the shop windows as quickly as he could, I watched him yank them past a tourist family that was scantily dressed in loud colors. Just after the FLDS girls passed the family, they turned their heads to sneak a double-take just as the 2 young tourist boys turned their heads to sneak a look back at them. It was as if both cultures had seen an unknown species of animal and couldn't believe their eyes. It was one of those "you had to be there" moments but the expressions were just priceless. I would have given anything to capture that moment, invasive or not.